The present invention relates to unsaturated polyester resin compositions which exhibit extremely low shrink, no shrink or even an expansion upon curing. The invention more particularly relates to shrink-controlled low temperature (about 0.degree. C. to about 50.degree. C.) curable compositions containing unsaturated polyester ("UPE") resin. The compositions are useful in a wide variety of contexts, such as pourable, self-levelling floorings, trowellable mortars, and joint sealing.
The fact that certain polymers shrink during curing is well documented. Unsaturated polyester resins, to which this invention is directed, commonly shrink from 5-15% in volume upon cure. Although such shrinkage can be tolerated in many situations, this is not always the case. Shrinkage in unsaturated polyester resin fabric reinforced composites can manifest itself as cracking, pitting, delamination or dimpling in the finished product. A self-levelling pourable flooring composition based upon unsaturated polyester resin may delaminate or shrink away from walls to leave undesirable gaps. Problems caused by shrinkage of unsaturated polyester resins used in other contexts are numerous and well known.
Chemical additives useful for controlling shrinkage during the curing of polymers such as unsaturated polyester resin systems are in demand. Although many such additives are known, including polyvinyl acetate, thermoplastic homopolymers and copolymers of butadiene, styrene, acrylonitrile, methyl methacrylate and ethylene, the search for new, effective shrink control agents continues. Accordingly, it is an object of the present invention to provide a novel shrink control agent for unsaturated polyester resins, especially when curing is desired at, or below, ambient temperatures.